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Tognacchini in a boat

Camilla Tognacchini’s field work captured the effects of human activities and tropical storms on the ecosystem of Heʻeia fishpond. (photo credit: Conor Jerolmon, UH Mānoa)

Original scientific research by two recent graduates from the University of Hawaiʻi at Mānoa’s Global Environmental Science (GES) undergraduate program has shed new light on Hawaiʻi’s past and current natural environment.

Present day stressors on a traditional Hawaiian fishpond

Camilla Tognacchini’s senior research project began with the goal to assess how the removal of invasive mangroves affects the health of Heʻeia Fishpond, a 600–800 year old productive fishpond on the windward side of Oʻahu. During the two-month study period, which included a mangrove removal effort, Tognacchini and mentor (oceanography professor Margaret McManus) monitored salinity, water clarity and water movement in the fishpond as well as weather conditions including rainfall, wind speed and direction and atmospheric pressure.

By fortune, the study period also captured the effects of three tropical storms—Wali, Iselle and Julio—thus expanding the scope of the study to include the effects of anthropogenic, as well as natural perturbations on the health of ecosystem.

Heʻeia Fishpond can serve as a model to quantify impacts of watershed management to the coastal ocean. The study indicates pond management, as well as watershed management, are essential in protecting coastal ocean resources.

Heeia fishpond

Watershed management is essential in protecting coastal ocean resources, including Heʻeia fishpond. (photo credit: Gilles Tisseraud)

Hawaiian fishponds are unique and advanced forms of aquaculture found nowhere else in the world. Hawaiian coastal waters have been, and continue to be, subject to major anthropogenic impacts from land use changes, which have altered the characteristics of the coastal environment.

“Increased ocean temperatures increase the frequency of tropical cyclones near Hawaiʻi,” said Tognacchini. “It is critical to have an understanding of how increased temperature and rainfall affect our coastal waters. With this understanding, areas like Heʻeia Fishpond can be properly managed to mitigate future climate variability.”

ʻŌhiʻa—a window to the past

ohia wood

Samples cut from a small wedge of ʻōhiʻa show promise in its use as an indicator of past climate conditions in the Hawaiian Islands. (photo credit: Justin Thayer)

From the curious mind to resource managers and community planners, many are interested in understanding how local climate has varied in the past. Scientists have long known that the form of carbon—that is, which isotope of carbon—a plant prefers to take in during photosynthesis can be influenced by environmental factors, such as rainfall.

As a GES student, Justin Thayer worked with mentor and oceanography professor Axel Timmermann to evaluate whether the carbon isotopic composition of ʻōhiʻa trees at Hakalau, Mauna Kea, Hawaiʻi could provide a reliable indicator of past climate conditions. Thayer and Timmermann’s work established that ʻōhiʻa may indeed be a window into historical conditions on Mauna Kea.

“Given the numerous parameters that influence the Hawaiian climate, elucidating the climate history of the Hawaiian Islands is pertinent to understanding and predicting future climate conditions. Since ʻōhiʻa grows in a wide range of climate types and given its potential long lifespan, the carbon isotope signature of ʻōhiʻa may be the perfect tool to provide high-resolution reconstructions of the climate history in the Hawaiian Islands,” said Thayer.

Preparing students for the future

The GES program at the UH Mānoa School of Ocean and Earth Science and Technology (SOEST) trains high-quality students to be knowledgeable in Earth-system science and think creatively about the challenges facing communities and natural resources now and in the future. As a GES degree requirement, each student performs original scientific research, writes a senior thesis and presents findings publicly. Mentors include SOEST faculty—global leaders in the fields of ocean, earth and space science.

Throughout the GES degree program, students are engaged in field work, laboratory work, and field trips, and have access to deep ocean and coastal research vessels, SOEST’s world-class Hawaiʻi Institute of Marine Biology, and an active volcano.

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